Physics IGCSE - Nuclear Physics

Composition of nucleus

Protons and neutrons

Proton number (Z)

no. of protons

Nucleon number (A)

total no. of protons + neutrons

Number of neutrons

A - Z

An element may have more than 1 isotope

Some isotopes are radioactive

Relationship between proton no. + relative charge on nucleus

Nucleus relative charge is 1+

Nuclear fission

A large unstable nucleus splits into smaller stable nuclei → releases energy and neutrons

Nuclear fusion

2 small nuclei join → form larger nucleus → releases energy

Ionising nuclear radiation

Radiation that removes electrons from atoms → turns them into ions

Background radiation

Naturally occurring ionising radiation from environment

Things that make a big contribution to background radiation

1. radon gas (in air)

2. rocks + buildings

3. food + drink

4. cosmic rays

How ionising nuclear radiation is detected

A Geiger-Müller tube connected to counter

Unit count rate measured in

Counts per second

Nature of alpha particle

Nature of beta particle

Nature of gamma particle

Alpha particle

Beta particles

Gamma particles

Radioactive decay

spontaneous and random change in unstable nucleus → result in emission of α particles or β particles and/or γ radiation

Change in nucleus due to α decay or β decay

Nucleus changes into different element → due to change in proton no.

Change in nucleus occurs during β emission

Neutron changes into proton + electron

Neutron → proton + electron

Decay equation for emission of α particles

Decay equation for emission of β particles

Half life

time taken for half the nuclei of that isotope in any sample to decay

Calculating half life in graphs

Half life undecayed population equation

Half life equation (count rate population)

Applications for radioactivity

(a) household fire alarms

(b) irradiating food → kill bacteria

(c) sterilisation of equipment using gamma rays

(d) measuring + controlling thicknesses of materials → less detection = thicker material

(e) diagnosis + treatment of cancer using gamma rays

Effects on ionising material on living things

1. Cell death

2. Cell mutation

3. Cancer

How radioactive materials are handled safely

• Time → minimize exposure time

• Distance → stay away from source

• Shielding → use lead or concrete barriers